Antennas provide for the radiation or reception of electromagnetic signals. An antenna may be characterized in terms of gain, beamwidth, or more specifically in terms of the antenna pattern which is a measure of the antenna gain as a function of direction. Simple antennas, such as dipoles or horns are well known, and find use in a number of applications. Simple antennas, however, are generally limited in terms of performance, providing limited gain/directivity and shaping of the radiation pattern.
Antenna arrays use a number of simple antenna elements to provide increased gain and directivity over what can be achieved using a single antenna element. In reception, signals from the individual elements are combined with appropriate phases and weighted amplitudes to provide the desired antenna pattern. Antenna arrays are also used in transmission, splitting signal power amongst the elements, again using appropriate phases and weighted amplitudes to provide the desired antenna pattern. Transmission lines or waveguides can be arranged to provide the desired phasing and combination/splitting of signals, and such an arrangement of transmission lines or waveguides is referred to as an antenna array feed.
At microwave frequencies, antenna feed design can be difficult when small element-to-element spacing relative to the wavelength is desired and potential for high losses. Microwave feed designs often use waveguide because of the lower loss provided. A waveguide feed typically includes a number of bends and twist sections to provide correct phasing to the elements of the array. These bends and twists take up large amounts of space, however, making waveguide feeds relatively bulky.
As a specific example, an antenna array can be constructed using horn antennas all facing in a common direction. The horn antennas are fed by a waveguide feed which includes a number of splitters and bends, for example in a corporate feed structure. The waveguide feed typically extends a large distance (i.e., many wavelengths) behind the antenna array. Typically waveguide feeds are designed for a specific array size (e.g., 1-by-8 array containing 8 radiating antenna elements), and as such, are not easily adapted to a larger array (e.g., 2-by-16 array containing 32 radiating elements) without significantly increasing the overall size and/or complexity of the feed network.